A cellular communication system includes three parts, namely, a user equipment (UE), a radio access network (RAN), and a core network (CN). The UE is a communication tool for network users, the RAN is responsible for managing air interface resources and is a part of mobility management, and the CN is responsible for user authentication, charging, mobility management, bearer setup and maintenance, and data routing.
The RAN before LTE (Long Term Evolution, long term evolution) includes a base station and a base station controller. For a GSM (Global System of Mobile communication) GPRS (General Packet Radio Service), the RAN consists of a BS (Base Station) and a BSC (Base Station Controller). For a UMTS (Universal Mobile Telecommunications System), the RAN consists of a NodeB and an RNC (Radio Network Controller). The base station communicates with the UE through an air interface, and the base station controller performs unified management and scheduling on multiple base stations. The LTE adopts a flat network architecture. The RAN has only one network element, that is, an eNodeB, which includes functions of a previous NodeB. The functions of the base station controller are also distributed to each eNodeB.
Since 3G (3rd Generation), distributed base stations have been widely applied, a distributed base station divides a conventional base station into a baseband unit (BBU) and a radio remote unit (RRU). The RRU implements such operations as radio signal receiving and transmission, peak-to-average power ratio reduction, digital pre-distortion, up-conversion, DAC (Digital-to-Analog Conversion)/ADC (Analog-to-Digital Conversion), and power amplification, and exchanges baseband information with the BBU through a Common Public Radio Interface (CPRI) protocol. Conventionally, physical connections between the BBU and the RRU mostly adopt fibers. The BBU+RRU mode makes the site deployment more flexible. The RRU is smaller in size and easy to deploy at such locations as an electric pole, and occupies a smaller space. Generally, inside a large-scale building, there are floors between layers, there are walls in rooms, and there are space partitions between indoor users. According to a BBU+RRU multi-channel solution, an RRU is deployed for each partitioned space by using such features. For a large-sized stadium with the floor area over 100,000 square meters, the stand may be divided into several cells, and each cell has several channels, with each channel corresponding to an RRU equipped with a panel antenna. The BBU is larger in size, and may be placed independently in an equipment room.
The mobile communication network generally uses a cellular structure, that is, different base stations are deployed at different locations, and each base bastion forms a cell and is responsible for communication of mobile users in the cell. To ensure that the mobile users can get seamless communication, neighboring cells have certain overlapping areas, so that the mobile users can hand over from one cell to another cell. In this conventional single-layer cell system, to increase the system capacity, the capacity of each cell needs to be increased, which is generally implemented by using complex and high-cost technologies. However, within a larger area, not all places need a very high capacity. In most cases, only a part of hot areas need a high capacity; for other areas with lower traffic requirements, even if a high capacity is provided, no users will use the capacity, which is a waste of system resources. That is, it is an inefficient manner to increase the capacity of the whole cell.
A better manner is to adopt a multi-layer cell structure (i.e., Heterogeneous Network in the LTE standard of the 3GPP, “HetNet” for short). That is, a macro cell is used to implement seamless coverage of the area, and then a Pico cell (i.e., Pico or Femto) is used at hot areas to perform overlapping coverage. The Pico cell provides a high capacity according to larger traffic requirements in the hot areas, so that the system capacity can be allocated according to the actual need. From the perspective of the system, this manner is a more accurate and purposeful capacity provision manner, and thus avoids the waste of the system resources. Currently, the HetNet is regarded as an important technical means to increase the system capacity in the LTE.
Most of the users are distributed in industrial areas during working hours, while most of users are distributed in residential areas during non-working hours. With this tidal effect of the users, the computing resources of the base station cannot be fully utilized. The purpose of proposing the architecture of a Cloud-RAN (C-RAN) is to utilize the computing resources of the base station in a more efficient way.
The C-RAN centralizes BBUs of distributed base stations in an area to form a BBU resource pool. Baseband signals of the RRUs in this area are processed in the same BBU resource pool. In this way, the mobility of users in this area does not affect the utilization of computing resources.
The centralized BBUs may be connected to the RRUs in a larger area through fibers. If bandwidth and time delays of interlinks between BBUs permit, the BBUs in the area may also be interconnected to form a BBU resource pool.
Because the BBU resource pool processes signals of multiple cells in a centralized manner, the C-RAN can also facilitate the joint transmission between the multiple cells.
However, in a conventional cloud-RAN architecture, one area and cell correspond to only one BBU resource pool, and all the RRUs need to be connected to the BBU resource pool through fibers. Because the physical distance is long and all the baseband signals must be sent to the BBU resource pool for processing, requirements for the transmission capabilities of fibers are very high.
In a HetNet scenario, if all the Pico cells need to be connected to a remote BBU pool through fibers, a large number of Pico cells may double fiber laying costs and data volumes to be processed by the BBU pool.
Compared with the conventional C-RAN architecture, the present invention has the following advantages: bandwidth for the connection between the base station and the cloud computing node is greatly saved. In future communication networks, the number of the Pico cells is several times the number of macro cells; the frequency band becomes increasingly wider; and the number of the antennas is increased dramatically from four to several dozens and even over one hundred. If the conventional cloud-RAN architecture is still used, it is a big challenge for fiber transmission to connect all baseband data to the cloud computing center several kilometers away.